Electronic article surveillance (“EAS”) systems are commonly used in retail stores and other settings to prevent the unauthorized removal of goods from a protected area. Typically, a detection system is configured at an exit from the protected area, which comprises one or more transmitters and antennas (“pedestals”) capable of generating an electromagnetic field across the exit, known as the “interrogation zone.” Articles to be protected are tagged with an EAS marker that, when active, generates a response signal when passed through this interrogation zone. An antenna and receiver in the same or another “pedestal” detects this response signal and generates an alarm.
In acoustomagnetic (“AM”) EAS systems, the key active element in the EAS marker is one or more strips of a melt-cast amorphous magnetic ribbon. When placed under a specific magnetic bias condition inside the marker, these strips receive and store magnetic field energy at its natural resonance frequency.
As a result, once the transmitted energy source from the transmitter in the detection system is turned off, the marker becomes a signal source and is capable of radiating an electromagnetic energy at its resonant frequency. Such a signal, even small can be readily detected by the receiver, due to the absence of the transmitting field.
Because of the nature of this process, other magnetic materials or metal in proximity to the EAS marker or the transmitter may interfere with the optimal performance of the EAS system. Conventional systems for detecting metals and magnetic materials are known, for example, U.S. Pat. No. 4,709,213, “Metal Detector Having Digital Signal Processing;” U.S. Pat. No. 5,414,411, “Pulse Induction Metal Detector;” and U.S. Patent Application Publication No. 2007/0046288, “Hybrid-Technology Metal Detector.”
Prior systems for using metal detection with EAS systems have also been suggested generally, for example, European Patent No. EP0736850, “Method for preventing shoplifting and electronic theft detection system.” However, systems such as these merely provide a metal detection system adjacent to an EAS system, but do not provide any mechanism for the increased efficiency and cost reduction of actually combining them into one system.
Therefore, what is needed is a system in which metal detection can be achieved by cohesively integrating metal detection functionality into an EAS system.